1. Technical Field
The present invention relates to a printer that executes a printing process on one side or both sides of a print medium, and to a control method for the printer.
2. Related Art
A thermal printer that prints the same content to two print media is known from the literature. See, for example, Japanese Unexamined Patent Appl. Pub. JP-A-H03-027434. JP-A-H03-027434 teaches a printer that advances receipt paper and journal paper, which are the two print media, by rotation of the paper feed roller with the print media in contact with the thermal head. By applying the same control signal to the heating resistors on two sides of the thermal head, the heating elements corresponding to the heating resistors are selectively caused to heat simultaneously and print the same print image to both the receipt paper and the journal paper.
Japanese Unexamined Patent Appl. Pub. JP-A-H04-001067 teaches a dot printer that disposes print heads on opposite sides of a single print medium and prints the same pattern from both sides. With the dot printer taught in JP-A-H04-001067, print heads having a plurality of printing wires are disposed opposite each other, and simultaneously print the same dot pattern from the front and back sides of the print medium conveyed between the two print heads. The force of impact of the printing wires of the print heads that print to the printing paper through an intervening ink ribbon is greater than the impact force of the printing wires of the print head that prints directly on the back side of the printing paper. This configuration improves copy performance and prevents damage to the printing paper.
Thermal printers that print on both front and back sides of a continuous print medium such as roll paper used for printing receipts are also known from the literature. See, for example, Japanese Unexamined Patent Appl. Pub. JP-A-S59-068268, Japanese Unexamined Patent Appl. Pub. JP-A-H03-0234560, Japanese Unexamined Patent Appl. Pub. JP-A-2007-320087, and Japanese Unexamined Patent Appl. Pub. JP-A-2008-006802. Duplex printing normally requires the printer to have at least a front print buffer to which data printed to the front (or first) side is buffered, and a back print buffer to which data printed to the back (or second) side is buffered. The print data is appropriately converted and written to the front print buffer and the back print buffer, and the printing process starts after the data required to print the front and back sides in a duplex printing mode has been buffered.
Japanese Unexamined Patent Appl. Pub. JP-A-2004-058488 teaches an inkjet printer that has a front print buffer and back print buffer and prints both sides in a duplex printing mode.
Print data is thus normally converted into the front print buffer to print on the front side of the print medium, and is converted into the back print buffer to print on the back side of the print medium. To print both sides simultaneously, the print data for both front and back sides is first written to the print buffers before printing starts. More buffer capacity is therefore required than a thermal printer that prints only one side.
Furthermore, when the start of printing is delayed until all of the print data has been written to the front and back print buffers, throughput before printing starts drops compared with when only one side is printed. More particularly, the same print data must be written to both the front print buffer and the back print buffer if the same content is to be printed on both front and back sides. However, if the time required to convert the same print data to both buffers can be shortened, throughput before printing starts can be further increased.